Many synthetic polymers have been developed and used in processes for the recovery of natural resources. Generally a desirable property is that such polymers impart to a liquid an increased viscosity when a relatively small quantity of the polymer is added, and preferably at a minimal cost. There is an increasing demand for such polymers which will withstand hostile environments including, e.g. high temperatures, high salinity and high content of multivalent metal cations, commonly known as "hardness ions", as well as the high acidity, temperature and shear conditions encountered in processes such as acid fracturing. Various polymers may be used in the processes for recovery or treatment of natural resources disclosed below as pertinent to this invention.